Technological advances in the design and manufacture of integrated circuits are revolutionizing microprocessor design. In the past, microprocessors and the like have consisted almost exclusively of digital circuits. Today, many integrated circuits such as microprocessors, are being designed to include analog and mixed-signal circuits.
During operation, digital integrated circuits produce noise throughout the substrate. This noise, sometimes referred to as "digital switching noise", adversely affects other sensitive digital or analog circuits integrated on the same substrate. Accordingly, analog (or sensitive digital) circuits included within a predominately digital environment are susceptible to digital switching noise produced by operation of the digital circuits. As more and more integrated circuits are being designed to include both digital and analog circuits (i.e. mixed signal integrated circuits), the inclusion of analog circuits increases the probabilities of performance degradation of the analog circuits caused by digital switching noise.
The effects of digital switching noise are becoming increasingly important due to the advanced semiconductor processes and materials used for integrated circuits. Improvements to semiconductor technology have included the construction of a relatively thin lightly doped epitaxial layer on top of a heavily doped layer. This improvement decreased problems associated with latch-up. However, the use of this type of semiconductor technology allows the coupling of noise throughout the substrate. Accordingly, the addition of sensitive analog (or digital) circuits to the integrated circuit increases the susceptibility of these circuits to noise problems.
Accordingly, there exists a need for a noise generator and method for generating noise that is representative of typical digital switching noise present in a completely digital, or predominately digital, integrated circuit. Further, there is needed a noise generator for generating noise for use in the evaluation and testing of analog and digital circuits relating to the effects of noise on such circuits. In addition, a need exists for a method of generating and applying noise for the evaluation of any possible performance degradation of an analog or mixed-signal integrated circuit to help determine the need for effective noise suppression techniques and design modifications of the circuit.